US5977480A - Grounding and RFI isolation for control station - Google Patents

Grounding and RFI isolation for control station Download PDF

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Publication number
US5977480A
US5977480A US08/900,493 US90049397A US5977480A US 5977480 A US5977480 A US 5977480A US 90049397 A US90049397 A US 90049397A US 5977480 A US5977480 A US 5977480A
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US
United States
Prior art keywords
door
cabinetry
cabinet
wall section
high frequency
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
US08/900,493
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English (en)
Inventor
Mark E. Timieski
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Elsag International BV
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Elsag International BV
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Filing date
Publication date
Application filed by Elsag International BV filed Critical Elsag International BV
Priority to US08/900,493 priority Critical patent/US5977480A/en
Priority to US09/378,424 priority patent/US6133652A/en
Application granted granted Critical
Publication of US5977480A publication Critical patent/US5977480A/en
Assigned to ELSAG INTERNATIONAL N.V. reassignment ELSAG INTERNATIONAL N.V. DOCUMENT PREVIOUSLY RECORDED AT REEL 010193 FRAME 0398 CONTAINED AND ERROR IN PROPERTY NUMBER 08900943. DOCUMENT RERECORDED TO CORRECT ERRORS ON STATED REEL. Assignors: TIMIESKI, MARK E.
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K9/00—Screening of apparatus or components against electric or magnetic fields
    • H05K9/0007—Casings
    • H05K9/0049—Casings being metallic containers
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K9/00—Screening of apparatus or components against electric or magnetic fields
    • H05K9/0007—Casings
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K9/00—Screening of apparatus or components against electric or magnetic fields
    • H05K9/0066—Constructional details of transient suppressor

Definitions

  • the present invention relates to the grounding and RFI isolation of control stations in general and more particularly to such control stations which have the need for remote location ground variation compensation and improved RFI isolation.
  • Control stations are known to have remote signal inputs thereto which may originate up to a mile from the station. This geographical difference causes ground potential differences which need to be considered. Also, in certain worldwide markets RFI isolation (containment of the RFI field within the cabinet) requirements are being made more stringent. This is especially true in the European market.
  • the ground connections must consist of a wide and short electrical connection to the chassis. This is to provide proper RF grounding of the door.
  • the grounding scheme should be an integral part of the door and chassis and should be simple to use requiring no disconnection to access the internal electronics.
  • the present invention solves the problems associated with prior art systems as well as others by providing an improved control station which compensates for geographical ground potentials and also has a very effective RFI isolation cabinetry.
  • the cabinet door openings have a conductive foil strip glued to the unpainted wall section of the metal cabinet opening of the control station.
  • the door covering this opening also has the same conductive foil strip glued to the unpainted mating wall section of the door abutting the cabinet wall.
  • a V-shaped conductive shielding gasket is located between the door and the cabinet wall sections to be compressed therebetween and to thus fill any gaps due to misalignment or warping of the door or cabinet wall sections.
  • the grounding is effected by having a large area stainless steel hinge mounted to the door to fit into the cabinet wall and be spring loaded thereto to allow the swinging down of the door. Also, a hybrid ground circuit is provided which grounds the DC at only one end of the circuit while grounding the AC signals at both ends of the circuit. The single end grounding eliminates geographical ground potential differences due to input signal locations to the cabinet which may be up to a mile distant from the cabinet.
  • one aspect of the present invention is to provide an improved RFI isolation system for control stations in high RFI environments.
  • Another aspect of the present invention is to provide a positive grounding of the control station compensating for the geographical ground potential differences resulting from remote signal inputs originally at long distances from the control station.
  • FIG. 1. is a side view of the distributed process control system control cabinet of the present invention.
  • FIG. 2. is a front view of the FIG. 1 cabinet showing the location of the conductive strip along the wall section of the front opening with the door removed.
  • FIG. 3. is a back view of the FIG. 1 cabinet showing the location of the conductive strip along the wall section of the back opening with the door removed.
  • FIG. 4. is a back view of the front door of the FIG. 1 cabinet.
  • FIG. 5. is a back view of the back door of the FIG. 1. cabinet.
  • FIG. 6. is an end view of the V-shaped conductive gasket fitting between the conductive strips of the cabinet and door.
  • FIG. 7. is a perspective view of a spring latch used to pen the cabinet doors of FIGS. 4-5.
  • FIG. 8. is a perspective view of a spring clip used to ground the door to the chassis.
  • FIG. 9. is a perspective view of spring latch of FIG. 7 mounted to swing open the doors of FIGS. 4-5.
  • FIG. 10. is a side view of the FIG. 9 assembly.
  • FIG. 11 is an exploded view of the latch section A--A of FIG. 10.
  • FIG. 12. is a perspective view of the ground circuit system located on the bottom of the FIG. 1. cabinet having two input and two output lines on opposite sides thereof electrically connected to a hybrid electrical circuit sealed in an elongated oval container.
  • FIG. 13 is a schematic of the hybrid electrical circuit of FIG. 11.
  • a distributed process control systems such as the ELSAG BAILEY SYMPHONY TM system which utilizes control stations 10.
  • These stations 10 comprise a work station 12 with a keyboard 14 thereon, a screen monitor 16 and a drive for floppy disks 18.
  • the station 10 has a cabinet 20 which is accessible by a front door 22 and a back door 24 both of which are hinged through a hinge assembly (not shown) of large area to help ground the cabinet.
  • the doors 22, 24 cover openings 25 leading to the inside of the cabinet 20.
  • the openings 25 have a formed metal lip or wall 26.
  • the doors 22, 24 also have a formed complimentary lip or wall 28.
  • the walls 26, 28 of both the doors and the cabinet are covered with an adhesive backed conductive film or strip 30 as described in CHOMERIC bulletin 210 entitled "CHO-MASK” Conductive Foil Tape with Pull-Off Mark” the content of which is incorporated herein by reference.
  • This tape is applied to the walls 26, 28 before they are painted by removing one side of the adhesive back therefrom and pressing the film 30 to the walls 26, 28.
  • the cabinet and walls 26, 28 are then painted.
  • a v-shaped conductive gasket 32 available from Grace company and identified as their "EMI Shielding Gasket for Commercial Electric Enclosures" described in their CHOMERIC Product Data Sheet for same is then glued to the doors 22, 24.
  • the door hinge 34 is manufactured from Stainless steel and then welded to the door 22 as best seen in FIG. 11.
  • the hinge 34 must be masked prior to painting the door 22 so that the hinge remains conductive.
  • the hinge could be bolted to the door 22 by bolts extending through openings 35 if welding stainless steel to the door is difficult.
  • the door hinge, conductive foil tape, and v-shaped conductive gasket are electrically connected through the unpainted sections of the door and cabinetry.
  • the hinge 34 makes electrical contact to the chassis 20 through the use of four spring clips 36 (2 for each hinge).
  • Each spring clip 36 is held to the chassis 20 by two screws 38 which mount the clips 36 along an opening therein, to have the spring clips 36 rub along the door hinge 34 as the door is inserted into channels 40 found in the chassis 20.
  • a stop bracket 42 is also used so that the door must be open to at least 30 degrees before it is removed. This prevents the off chance that a high potential wire is near the door perimeter and it comes into contact with the door as it is opened. The person removing the door has a clear view into the console before removing the door.
  • RFI isolation is provided by the isolation assembly 34 shown in FIG. 11.
  • This assembly 34 has a pair of inputs from signal sources that may be up to a couple of kilometers from the cabinet 20. This geographical distance may result in the occurrence of a potential being developed due to differences in ground potential between these geographically distant locations. This voltage potential may cause heating of the input wires which may burn up the signal lines. Thus the inputs are filtered through a electrical hybrid ground circuit 42 as shown schematically in FIG.13. This circuit eliminate these ground potential differences and prevents the danger of signal wire deterioration due to the wire heating generated by these potential differences.
  • the circuit assembly 44 is best seen in FIGS. 12 and 1.
  • the assembly 44 is mounted inside the cabinet 20 through a bottom aperture 46 found at the back of the cabinet 20. The mounting is done through screw slots 48 found on the flanges 50 of the assembly 44 in a known manner.
  • the hybrid electrical assembly 42 is encased in cases 50 with the cases 50 screwed into holes 52 located on a bottom flange 54 of the assembly 44.
  • a case 50 cover 56 is screwed into the main body 58 of the assembly 44 by screws 60 in a known manner.
  • the main body 58 as well as the cover 56 has apertures 62 and slip rings 64 through which input and output loop connectors 66 are extended and connected to the body by flanges 68 and nuts 70 on opposite sides of the body 58 in a known manner.
  • the assembly 44 provides for two field inputs and two outputs comprising a pair of loop inputs and outputs as best seen in FIG. 13.
  • the loop inputs and output are connected to the circuit through shielded connectors as is known in the art to thus have the ground for DC signals going through one end while the AC is grounded at both ends.
  • the present design uses "N" style pass through bulkhead connectors.
  • the transmit side 72 or input of each loop is hard grounded through the keyholes 64 which are connected to the chassis 22 through the metal body 58 connection.
  • the receive side 74 is capacitively coupled with a 1 microfarad and 0.05 microfarad capacitor to chassis 22.
  • the 1 microfarad capacitor is designed for use in application such as this where very large transient voltages may occur. While the capacitor is rated for 250 vac. it can handle voltage transients in access of 1 KV. While this capacitor can handle large voltages, it provides poor capacitance at the frequencies of interest (30 to 250 MHZ) as this capacitor is mostly inductive. This capacitor must survive due to low frequency transients. Thus the smaller capacitor is provided which will do the bulk of the work at the higher frequencies.
  • the small bracket assembly 44 is designed so that the cables can be connected horizontally or the cables can come through the floor of the console 22 and connect vertically to the assembly.
  • the present assembly provides DC grounding at one end to prevent "ground loop" where the variance in ground potential could cause the cable to heat up and AC grounding at both ends to provide RF shielding.

Landscapes

  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
  • Casings For Electric Apparatus (AREA)
US08/900,493 1996-09-30 1997-07-25 Grounding and RFI isolation for control station Expired - Fee Related US5977480A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US08/900,493 US5977480A (en) 1996-09-30 1997-07-25 Grounding and RFI isolation for control station
US09/378,424 US6133652A (en) 1996-09-30 1999-08-20 Grounding and RFI isolation for control stations

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US2711696P 1996-09-30 1996-09-30
US08/900,493 US5977480A (en) 1996-09-30 1997-07-25 Grounding and RFI isolation for control station

Related Child Applications (1)

Application Number Title Priority Date Filing Date
US09/378,424 Division US6133652A (en) 1996-09-30 1999-08-20 Grounding and RFI isolation for control stations

Publications (1)

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US5977480A true US5977480A (en) 1999-11-02

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US08/900,493 Expired - Fee Related US5977480A (en) 1996-09-30 1997-07-25 Grounding and RFI isolation for control station
US09/378,424 Expired - Fee Related US6133652A (en) 1996-09-30 1999-08-20 Grounding and RFI isolation for control stations

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US (2) US5977480A (de)
EP (1) EP0833553A3 (de)
CA (1) CA2215979C (de)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6133652A (en) * 1996-09-30 2000-10-17 Elsag International N.V. Grounding and RFI isolation for control stations
US6271465B1 (en) * 1999-08-31 2001-08-07 Nokia Mobile Phones Limited Low cost conformal EMI/RFI shield
US6355878B1 (en) 1999-12-24 2002-03-12 Expan Electronics Co., Ltd. Clip type conductive gasket
US20030209355A1 (en) * 2001-08-21 2003-11-13 Dell Products L.P. Perforated EMI gasket
US20050265003A1 (en) * 2004-05-07 2005-12-01 Giovanni Coglitore Electromagnetic interference shield for I/O ports
US9124049B2 (en) 2013-03-13 2015-09-01 Silicon Graphics International Corp. Micro ethernet connector

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7927147B1 (en) * 2009-12-15 2011-04-19 Hewlett-Packard Development Company, L.P. Connector assembly
US20120145450A1 (en) * 2010-12-08 2012-06-14 Ezconn Corporation Shielding device
WO2014071021A1 (en) * 2012-10-31 2014-05-08 Adc Telecommunications, Inc. Anchoring cables to rack with cable clamp arrangements
CN110248478A (zh) * 2019-06-14 2019-09-17 大连亚太电子有限公司 一种pcb电路布线方法

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5142101A (en) * 1990-11-29 1992-08-25 Kitagawa Industries Co., Ltd. Electromagnetic-shielding gasket
US5262588A (en) * 1992-01-07 1993-11-16 International Business Machines Corporation Electromagnetic interference/radio frequency innterference seal

Family Cites Families (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4187481A (en) * 1977-12-23 1980-02-05 Bunker Ramo Corporation EMI Filter connector having RF suppression characteristics
US4386819A (en) * 1981-08-31 1983-06-07 Amp Incorporated RF Shielded assembly having capacitive coupling feature
US4551633A (en) * 1983-06-24 1985-11-05 Itt Corporation Electronic grounding system for electrical distribution systems
US5070216A (en) * 1990-04-27 1991-12-03 Chomerics, Inc. Emi shielding gasket
US5170008A (en) * 1991-08-29 1992-12-08 International Business Machines Corp. External cable grommet for cable entry of EMI protected cabinets
SE469151B (sv) * 1991-09-27 1993-05-17 Ericsson Telefon Ab L M Skaermad rfi-genomfoering
US5627898A (en) * 1993-11-19 1997-05-06 Washino; Kinya Signal distribution with user-configurable ground-loop control
US5477188A (en) * 1994-07-14 1995-12-19 Eni Linear RF power amplifier
US5977480A (en) * 1996-09-30 1999-11-02 Elsag International N.V. Grounding and RFI isolation for control station

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5142101A (en) * 1990-11-29 1992-08-25 Kitagawa Industries Co., Ltd. Electromagnetic-shielding gasket
US5262588A (en) * 1992-01-07 1993-11-16 International Business Machines Corporation Electromagnetic interference/radio frequency innterference seal

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6133652A (en) * 1996-09-30 2000-10-17 Elsag International N.V. Grounding and RFI isolation for control stations
US6271465B1 (en) * 1999-08-31 2001-08-07 Nokia Mobile Phones Limited Low cost conformal EMI/RFI shield
US6355878B1 (en) 1999-12-24 2002-03-12 Expan Electronics Co., Ltd. Clip type conductive gasket
US20030209355A1 (en) * 2001-08-21 2003-11-13 Dell Products L.P. Perforated EMI gasket
US6858794B2 (en) * 2001-08-21 2005-02-22 Dell Products L.P. Perforated EMI gasket
US20050265003A1 (en) * 2004-05-07 2005-12-01 Giovanni Coglitore Electromagnetic interference shield for I/O ports
US7411784B2 (en) * 2004-05-07 2008-08-12 Rackable Systems, Inc. Electromagnetic interference shield for I/O ports
US9124049B2 (en) 2013-03-13 2015-09-01 Silicon Graphics International Corp. Micro ethernet connector
US9461422B2 (en) 2013-03-13 2016-10-04 Silicon Graphics International Corp. Micro ethernet connector

Also Published As

Publication number Publication date
US6133652A (en) 2000-10-17
EP0833553A3 (de) 1998-04-08
CA2215979A1 (en) 1998-03-30
CA2215979C (en) 2001-11-13
EP0833553A2 (de) 1998-04-01

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Free format text: DOCUMENT PREVIOUSLY RECORDED AT REEL 010193 FRAME 0398 CONTAINED AND ERROR IN PROPERTY NUMBER 08900943. DOCUMENT RERECORDED TO CORRECT ERRORS ON STATED REEL.;ASSIGNOR:TIMIESKI, MARK E.;REEL/FRAME:015641/0416

Effective date: 19970723